Placebo's Effect May Depend on Your Genes

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Your response to placebos, or dummy medicine, may depend on your
genes, according to a new study.

People with a gene variant that codes for higher levels of the
brain chemical dopamine respond better to placebos than those
with the low-dopamine version.

The findings, reported online Oct. 23 in the journal PLoS One,
could help researchers design medical studies that distinguish
the placebo response from the underlying effect of a medicine
— the real aim of drug trials.

"This is a possible way to discern who is going to be a placebo
responder or nonresponder in a clinical trial," said study
co-author Kathryn Hall of Beth Israel Deaconess Medical Center in
Brookline, Mass.

People report feeling better
after receiving a placebo, such as a sugar pill or fake
treatment, for conditions ranging from chronic pain to
Parkinson's disease. But only some patients respond strongly, and
there's no way to predict who will improve on a placebo.

A few studies have provided clues. Differences in versions of the
catechol-O-methyltransferase (COMT) gene, which determines levels
of
dopamine in the brain's prefrontal cortex, are linked to
differences in reward-seeking and pain perception. People with
the high-dopamine version, or allele, of the COMT gene feel pain
more acutely and seek rewards more strongly than those who have
the low-dopamine copy.

That led the researchers to wonder whether the gene modulates
placebo response.

To find out, Hall and her colleagues analyzed DNA from 104
patients with irritable bowel syndrome who were randomized to one
of three groups: One was told they were on the waiting list for
treatment, another received a placebo in the form of seemingly
real, curt acupuncture, and the third group received fake
acupuncture from a caring, warm practitioner who looked
patients in the eye, asked about their progress, and even touched
them lightly, Hall told LiveScience.

Patients with the high-dopamine version of the gene felt slightly
better after seeing the curt, all-business health-care provider
that gave placebo acupuncture. But they were six times as likely
to say their symptoms improved with a caring practitioner as
those with the low-dopamine gene, who didn't improve much in any
group.

The findings suggest that medical studies called clinical trials
could identify treatment versus placebo effect by grouping
patients by gene variant, Hall said. Knowing up front the level
of placebo effect for a clinical trial could reduce the cost of
the trial significantly by using fewer participants, for
instance, she said.

People with the high-dopamine allele of the gene may do well on
the placebo with the nurturing treatment because they are
generally more attuned to their environments, said University of
Michigan psychiatrist Jon-Kar Zubieta, who was not involved in
the study.

"It speaks about an interaction between the environment and the
gene," Zubieta said. "It's very possible that individuals with
this allele are more able to process those positive environmental
cues."